Compared to sealed (i.e., “paved”) roads, unpaved roads are relatively easy and inexpensive to build because their construction does not require large machinery to pour the base material or to create a sealed surface. However, the maintenance of unpaved roads has been perpetually plagued by surface deterioration and loss of surface cohesion and road compaction due to traffic and weather. The impact of water on unpaved roads is especially pronounced because the quality of the surfacing materials is lower than in paved roads, and thus provides reduced surface protection from the elements. Water can also seep into the road base from the sides and bottom of the road's base or sub base. Unpaved roads require much more frequent maintenance as compared to paved roads, particularly after wet periods or when faced with increased traffic.
Surface deterioration is typically evidenced by “dust,” which results from the loss of fine binder material from road surfaces. Dust is a substantial problem for unpaved roads, not only due to decreased road visibility, but also because the loss of these fine materials leads to other types of road distress such as loss of cohesion and compaction of the road fill material. This can create potholes and road imperfections that damage vehicle tires. Compaction and dust formation are exacerbated by high traffic conditions and heavy traffic loads.
Mining operations in particular require frequent and heavy traffic over unpaved mine haul roads. In mining operations, the mined minerals must be transported within the mine site for efficient processing. With the efficiency of modern digging equipment, tons upon tons of mineral can be quickly excavated. The excavated material is transported from the excavation point to a central processing location by truck. The more mature the mine, the longer the distance from the excavation location to the processing location. While the trucks are capable of transporting vast quantities of material in a single load, the trucks are large, heavy, and capable of creating large amounts of dust as they are driven over the roads. Further transportation is required in transporting mine waste materials, during mine reclamation, and for various other mining activities.
Typically, the mine haul roads are built with crushed aggregate from the material being unearthed, which is readily available at the mining site. It is not practical to pave the roads at an excavation site, as the excavation equipment is moved constantly and would require additional road building nearly every day. This constant road building would interrupt the flow of digging, which is carefully planned in consideration of both efficiency of removal and the safety of the road's underlying bed. Also, substantial portions of the mine haul roads are eventually mined and processed in a mineral processing plant.
Mine haul roads typically have poor water retention, and the trucks create large areas of dust when driving over the roads. The trucks continuously drive over the roads moving the minerals from the location of mining to the processing location. In this process, the weight of the heavy trucks crushes the aggregate material into finer and finer material that can be easily lifted by the truck tires. If the mine is subjected to any wind, the dust can be transported very quickly to surrounding areas. The dust can then saturate the mine and surrounding areas with airborne particulates.
When a vehicle is to be used in a high dust environment, special air filters are employed that are expensive to install and need critical maintenance to assure that no damage to the filter has occurred that would allow ingestion of the dust into the engine.
In mining operations, the unpaved roads are typically maintained by periodically spraying water onto the road surface. For example, a water truck drives over the unpaved roads and dispenses water over the road surface. It is not uncommon for a mine to spray 250,000 gallons of water a day over the roads. Although water is used to maintain the roads, the water itself can damage the road. Indeed, rain can degrade road surfaces. In particular, watering results in road surface deformation (e.g., ruts, corrugations, depressions, and potholes), as well as washing away of fine materials required for surface smoothness and optimum surface shape. As a result, more frequent road grading is required.
Mine haul roads are regulated based on industry standards for (1) new road construction; (2) frequent watering of existing roads to minimize the impact of dust on vehicle speed, production, health, and safety; and (3) grading roads as needed to maintain the optimum shape and surface smoothness for reduced haul truck tire wear and maximum safe driving speed. In order to abide by industry guidelines, mines will incur significant costs associated with purchasing, operating, and maintaining a fleet of mine water trucks and road graders (e.g., water, fuel, lubricants, filters, tires, and truck operator salary and benefits). In water scarce regions, the mine will also have to obtain the necessary water rights and pay to pump the water over a long distance. These costs can be a sizable expense.
Chemical road dust suppressants often are not a viable option for treating mine haul roads because treatment with these suppressants requires that the road be “prepared” prior to treatment and closed during application of the suppressant, which reduces mine production. Furthermore, the large amount of chemical used to stabilize the road can have a negative impact on the mineral processing plant when the road is later mined and processed.
In sum, mine haul roads require frequent maintenance to ensure optimum safety and productivity and to satisfy industry guidelines. This maintenance includes frequent watering using properly designed water trucks, and frequent grading to maintain an optimum road bed shape and smooth surface. A typical large U.S. mine has a mine haul road maintenance budget of millions of dollars per year. By improving mine haul road maintenance and operations through reducing the frequency of watering, mine operation costs can be significantly reduced.